Process and apparatus for coating



y 12, 1931- e. A. JOHNSON 1,804,991

PROCESS AND APPARATUS FOR COATING Filed Dec. 20, 1928 avweutoz El iot nuPatented May 12, 1931 PATENT OFFICE UNITED STATES GUSTAVE A. JOHNSON, ormvmeron, NEW .TEEsEY, ASSIGNOR 1'0 AMERICAN STEEL PIPE co. mo. ormvme'ron, NEW TEEsEY, A CORPORATION or NEW .TEEsEY PROCESS AN DAPPARATUS FOR COATING Application filed December 20, 1928. Serial No.327,250.

This invention relates to the art of coating metal surfaces with metal,for example, coating a metal which is subject to various injuriousefiects with another metal which is 5 not to any extent subject'to theseefiects.

One of the objects of the invention is to put upon a metal object ametallic coating which is highly resistant to deleterious atmospheresand exacting physical actions. When uncoated metals such as iron orsteel are laced in atmospheres containing strong acid umes, ammonia gas,steam or other oxidizing vapors, salt spray and the like, they quicklydeteriorate. Even when coated with enamel,

zinc or other common protective agents, the

metals under such severe conditions, deteriorate almost as rapidly as ifuncoated.

Aluminum among other metals has been found to resist the action of theseatmospheres to a high degree. Aluminum is named in the presentdisclosure because it is the most common and inexpensive of the classand resists a great number of the injurious effects which it is commonlynecessary to guard against.

The manner in which aluminum is applied to surfaces, however, largelydetermines the effectiveness of the coating and-what is equallyimportant-affects the cost of its apao plication. Put on in certainways, the aluminum coating readily separates from the base and fallsoif, particularly if the base be bent or otherwise distorted; or thecoating willcraok; or is full of pin holes even when relatively thick asa whole; or is not sulficiently hard and tough to withstand abrasiveefl'ects. Furthermore, according to certain methods of application,those partsof the objects which are somewhat inaccessible will not beproperly coated. Thus, the interior of pipes is fre ently left uncoatedor is coated only a short distance from each end.

Again, the coating may not be uniformly applied to all of a number ofobjects being treated or even may not be uniformly applied to the entiresurface of a single object.

With the above and other considerations in view, one specific embodimentof the invention will now be particularly described, it being distinctlyunderstood that there isno intention to limit the scope of the inventionin any respect by such a particular description. In this descriptionreference will be made to certain illustration found in the accompanyingdrawing wherein the single fi ure is a sectional elevation of apparatusor dipping elongated objects such as ipes.

The articles to be coate are first thoroughly cleaned and freed fromdirt, ease, scale or other surface adhesions. I iron pipes are to becoated the are subjected to a pickling action as by eing dipped whilesuspended at a slight inclination to the horizontal in a bath of a 5%solution of sulphuric acid. Following this the pipes are dipped while sosuspended in an alkaline bath which preferably is heated. Successivedippings in clean water remove the alkali and all remaining traces ofacid. The water is preferably quite hot, perhaps 180 F., to heat thepipes so that when they are later drained in a nearly vertical positionthe heat of the pipes causes the water film to be evaporated. Thus whenthe pipes stop steaming it can be safely assumed that they arethoroughly if necessary a stiff brush may be pulled through the pipes toremove any articles which have been loosened but left t erein.

For objects other than iron pipes the cleaning process should be equallythorough, the kind of process being that best suited to the particularobject being treated.

Next the objects are given an application of the aluminum coatingpreparation and allowed to drip. Preferably the objects are dipped whilesuspended with their longer dimensions vertical.

The dipping li uid requires particular consideration as the ind ofvehicle with which the alminum powder is mixed greatly affects thecharacteristics of the final coating. Some of the outstandingrequirements for the vehicle are: That it will thoroughly wet thesurface; that it will not dry too quickly; that it will when dried behard and tough; that it will withstand relatively high temperatureswithout becoming brittle, discolored and without completely evaporating;that when dried the residual film will -successfully tice undertaken upto the present time.

withstand the atmospheres which the aluminum itself is expected towithstand; that when heated will promote the proper disposition orleafing of the aluminum particles; and that throughout the time thealuminum powder is mixed therewith will effectively prevent oxidationthereof, any oxidation of the aluminum hindering the combination of thealuminum coating with. the base metal.

I have foundthat an oleo-resinous vehicle which evaporates to the extentof about 55% leaving about 45% residue as a film with the aluminumpowder gives best results in Hui;

no a vehicle, to give an example,'may be made of a mixture of China-woodoil, linseed oil, certain gums such as East India gum, Kauri gum orester um, and certain metal salts such as the safts of lead, manganeseor cobalt which act as catal zers.

The aluminum pow er employed is of the kind which has been ground underconditions suitable for preventing surface oxidation of the particlesand which has been preserved until ready for mixing with the liquidvehiclein such a way as to maintain the nonoxidized condition of thesurfaces of the particles. The methods of thus reserving the particlesforms no part of t e present invention, it being merely understood thatsuch un-oxidized aluminum powder is to be used, and that the materialused to preserve the particles will not be injurious to the finalcoating as obtained by the present process.

The aluminum powder is thoroughly mixed into the vehicle, preferably soas to leave the final mixture relatively thin. While the proportions mayvary greatly good results have been obtained by a mixture made up in theratio of two pounds of aluminum powder to each gallon of liquid vehicle.

As stated above the articles may be dipped into this coating material,with constant agitation to keep the aluminum powder thoroughl mixed in.Dipping is generally preferre but so far as some of the other steps ofthe process are concerned the mode of application may in some cases beother than by dipping.

If, for example, tubes or pipes are to be dipped they may be suspendedby one end and lowered vertically into an elongated tank of liquid. Inthe figure, a plate 10 carries a group of pipes 11, care being taken tokeep the pipes separated from each other at all times. These pipes areshown immersed in a bath of the coating liquid standing to the line 12in a tank 13. If the interior of the pipes is not to be coated theendsmay be plugged. The pipes shown are receiving an inside coating as wellas an outside coating. Indeed, the present process and apparatus reespecially designed to give a perfect e as well. as outside coatingwhereas previously the inside coating has been but indifierentlyapplied. a

The aluminum particles have a pronounced tendency to settle to thebottom of the bath as well as to collect into lumps. To prevent this apump 14. of the gear type is employed to crush the lumps, to thoroughlymix the articles with the liquid vehicle and aswill be explainedpresently to assist in getting proper and even application of thecoating upon the pipes or other articles suspended in the tank.

The ipes do not extend to the bottomof the tan but leave a space inwhich the discharge pipe 15 of the pump terminates, the same beinginclined upwardly and bent to lie tangentially within the walls of thetank. In other words the pipe is spiraled upwardly. This produces awhirling upward circulation of the liquid causing it to flow through thepipes and uniformly about them in the most advantageous manner. Liquidmay be withdrawn from the tank through the pump suction pipe 16 the endof which is located intermediate the length of the tank.

While either the bath or the dipped articles may be heated, the bathemployed is such that good results may be obtained even in very coldweather without heating. If heat is applied it will not be a high heatas this would tend to evaporate part of the bath. This is not desiredfor the reason that such evaporation makes it difiicult to keep the bathat the desired uniform and known quality and consistency. Moreover, thelater steps of the process insure the proper spreading and-uniformdistribution of the coating even if the dippin should leave slightlythickened spots or curtains.

After the articles have been dipped they may be allowed to drip over thetank, after which they are transferred to a suitable oven Where thecoating is baked on before it has had an opportunity to dry.

The oven employed preferably contains a non-oxidizing or reducing orinert atmosphere. Where the oven is heated by gas the carbon dioxideproduced by the gas burners may be suflicient for the purpose. However,with the coating vehicle used which is to a certain extent non-oxidizingsatisfactory results might be obtained even in an oxidizing atmosphere,for example air or steam.

Further, the oven may be provided with wlndows of proper size and colorto assist the bakin although good results have been obtaine in a darkoven.

The temperature of the oven is maintained sufiiciently high to dry andset the coating but is kept below the carbonizing temperature of thevehicle used in the coating composition. For example, a temperature of275 to 325 degrees F. applied for one hour has been found satisfactorywhere another coat is later applied and baked say at a temperature of350 to 375 degrees F. for two hours. If only one coat is desired eitherthe temperature or time of baking may be increased. When two or morecoats are applied the heat emplo ed to bake the later coat or coats alsofurt er bakes the first coat and it is for this reason that the heatingof the first coat is kept below the amount which would otherwise berequired.

It has been found that the heating completely dissipates all curtains inthe coating and leaves it uniform and thin so as to follow all contoursof the article coated.

When the coating is applied according to this process the aluminum asshown by tests appears to have penetrated the surface and to some extentto have alloyed with the base metal, while part of the aluminum iscarried in the thin film or non-oxidizable vehicle residuum.

The coating is extremely tenacious and shows no flaking or separationeven when the coated article is severely bent, hammered, stretched orotherwise distorted.

While the specific embodiment chosen relates to the coating of pipes orthe like, the process is ap licable to sheets, wires and various other 5apes.

It is to be understood that various modifications and changes may bemade within the spirit of the invention as expressed in the appendedclaims.

What I claim is:

1. The method of coating metal objects with aluminum which comprisescoating the objects with a bath containing finely divided aluminum and avehicle including linseed oil, Ghinawood oil, a resinous gum and amineral salt, thereafter baking the coat thus applied in an oven atapproximately 300 F., for one hour, applying a second coat of the samematerial and baking in an oven at approximately 350 F. for two hours.

2. The method of coating pipes which comprises suspending the pipesvertically within-a coating bath containing a powdered metal andagitating the bath from the bottom to give it an upward swirling motionso as to enter the interior of the pipes as well as to evenly coat theirexterior surfaces.

3. The method of coating pipes with aluminum which comprises dipping thepipes vertically in a tank containing a bath of aluminum powder and aliquid vehicle, which bath is circulated upwardly with a whirling motionfrom below the pipes so as to enter the interior of the pipes and toevenly flow over the exterior of the pipes.

4. The method of coating metal objects with a coating metal whichcomprises applying a coat of finely divided metal suspended in a liquidvehicle to the surface of the object and baking below the carbonizingtemperature of the vehicle for a length of time sulficient to produce asurface alloying of the coating metal with the base metal; applying asecond coat of the same material and ba 'ng it at a relatively highertem erature below the carbonizing temperature or a longer period oftime.

In testimony whereof, I have signed my name to this specification this18th day of December 1928.

GUSTAVE A. JOHNSON.

